原式
=1/17×5×1/6+1/17×4×5/19+1/17×7×5/18
=5/17×1/6+5/17×4/19+5/17×7/18
=5/17×(1/6+4/19+7/18)
=5/17(3/18+7/18+4/19)
=5/17(10/18+4/19)
=5/17(5/9+4/19)
=5/17×131/171
=655/2907